PUD & GERD Flashcards
GASTROINTESTINAL DRUGS
The neural pathway delivers acetylcholine which is released from
postganglionic nerve terminals.
Gastrin is released from antral G-cells located in the antrum and
duodenum and delivered to the parietal cell via the systemic
circulation.
Histamine is released from mucosal mast cells into the interstitial
fluid via the paracrine pathway.
Pepsinogen is a proenzyme that will form pepsin in an acidic
environment, and it combines with acid to form a proteolytic
complex that further aids in the digestive process.
Histamine H2 receptor antagonists drugs & use
cimetidine + tidine
peptic ulcers: all four drugs are equally effective in promoting healing of gastric and duodenal ulcers and provide an overall healing rate of 70-95%; without concurrent H. Pylori eradication treatment, there is a high risk of recurrence of the ulcer (60-100% of cases)
ii. GERD
Histamine H2 receptor antagonists moa & pharmacokinetics
these drugs block the actions of histamine on histamine H2 receptors; in the stomach they
inhibit gastric acid secretion
induced by histamine, and to a lesser extent inhibit gastrin and muscarinic receptor
stimulated acid secretion
all given orally; nizatidine has a higher bioavailability (about 90%) than the others (about 50%)
because nizatidine does not undergo much first-pass
metabolism; potency of the drugs is famotidine > ranitidine = nizatidine >
cimetidine
Histamine H2 receptor antagonists adverse effects
limited CNS effects; since cimetidine inhibits P450 enzymes it can slow metabolism and potentiate the action of several drugs (ex: warfarin, diazepam, phenytoin, quinidine, carbamazepine, theophylline, imipramine); also, cimetidine may have antiandrogenic effects which may lead to gynecomastia (also a P450 effect); overall incidence of side effects is low due to limited function of H2 receptors in other tissues; headache, dizziness, and nausea have been observed
Inhibitors of the H+ /K+ –ATPase proton pump
drugs & use
omeprazole, lansoprazole, rabeprazole, pantoprazole,
esomeprazole (S-isomer of omeprazole)
therapeutic use: treatment of active ulcers; reflux
esophagitis; long-term treatment of hypersecretory conditions
(Zollinger-Ellison); in combination with antimicrobial agents
to eradicate H. Pylori
Inhibitors of the H+ /K+ –ATPase proton pump moa & kinetics
inhibit gastric acid secretion by
irreversibly blocking the proton pump; since the action of the
drugs is irreversible, the inhibition of gastric acid secretion
lasts long after the drug has been eliminated
All PPIs are prodrugs
and must be converted
to the active form. Irreversible covalent bond
given orally as delayed-release capsules
(Note: these drugs are stable at neutral pH but are destroyed
by gastric acid; therefore, if the gelatin-coated capsule is
broken prior to swallowing the drug will be destroyed; if
taken properly, the drug will be released from the capsule in
the intestine where it is rapidly absorbed); omeprazole,
inhibits P450 enzymes and can affect metabolism of warfarin, phenytoin, diazepam, and cyclosporine
Inhibitors of the H+ /K+ –ATPase proton pump adverse effects
well-tolerated; about 3% of patients experience GI effects such as nausea, diarrhea, and abdominal colic; do not use with clopidogrel (effect)
Eradication of H. Pylori
a. combination therapy is used: PPI + 2 antibiotics
b. therapeutic use: eradicates H. Pylori in 90% of
patients to aid in ulcer treatment
c. mechanism of action: kills the bacteria (see mechanisms
for metronidazole, clarithromycin, amoxicillin, tetracycline)
MCAT
Prostaglandins drugs & use
misoprostol
prevent gastric ulcers caused by NSAIDs;
less effective than the H2 receptor antagonists in treating
peptic ulcers; available in combination with diclofenac
(Arthrotec)
Prostaglandins moa & adverse
mechanism of action: is a prostaglandin E2 and I2 receptor
agonist so it will decrease cAMP levels and inhibit acid; stimulates mucous and bicarbonate production
adverse effects: diarrhea, abdominal cramping; abortion, premature birth, birth defects (cat. X)
Antimuscarinic agents
hyoscyamine, dicyclomine, glycopyrrolate
therapeutic use: adjuncts in peptic ulcer treatment
mechanism of action: block muscarinic receptors which
inhibits gastric acid secretion
adverse effects: atropine-like (limits use of these drugs)
Antacids
aluminum hydroxides and magnesium hydroxides, calcium
carbonates (Tums, Rolaids); sodium bicarbonate; Al(OH)3 +
Mg(OH)2 + alginic acid (Gaviscon)
therapeutic use: promote healing of gastric ulcers; relieve
symptoms of GERD
antacids moa
the antacids react with gastric acid
to produce water and a salt; antacids also reduce pepsin
activity by increasing the pH (pepsin activity decreases
as pH increases); Gaviscon is not as effective as the others
at neutralizing acid but does form a highly viscous
solution which acts as a mechanical barrier to reflux and
protects the mucosa
antacids adverse
aluminum hydroxide may cause
constipation; magnesium hydroxide may cause diarrhea; bicarbonates have the potential to cause systemic alkalosis, liberate CO2 which causes belching and flatulence; the sodium content of antacids is important in patients with hypertension of congestive heart failure
antacids drug interactions
it is advisable to avoid concurrent
administration of antacids and other drugs since antacids can
affect absorption; sodium bicarbonate is used to alkalinize
the urine
Take antacids 2 hours before or after other drugs
